In instances in which a radio resource control (RRC) connection has been lost, an RRC connection re-establishment procedure may be conducted in an effort to re-establish the lost connection. The connection re-establishment procedure searches for a cell, such as a base station, e.g., an eNode B (eNB), that is suitable for supporting the radio connection. In this regard, a suitable cell is generally defined as a cell for which the mobile terminal has access privileges, such as a cell operated by or otherwise under the control of the network operator with which the mobile terminal is associated.
By way of an example, the Evolved Universal Mobile Telecommunication System (UMTS) Terrestrial Radio Access Network (E-UTRAN), which is also known as Long Term Evolution (LTE) or 3.9 G includes a cell selector timer that dictates the length of time that is devoted to cell selection during an RRC connection re-establishment procedure. In this regard, the timer may be set to a predefined value, such as 30 seconds, and the mobile terminal may then search for a suitable cell to support the RRC connection re-establishment. In instances in which the timer expires prior to the mobile terminal selecting a cell, the RRC connection re-establishment procedure may be terminated. However, if the mobile terminal selects a suitable cell prior to expiration of the timer, the timer may be stopped and the RRC connection re-establishment procedure may be continued.
Mobile terminals and the underlying communications network are also configured to facilitate emergency call handling, such as 911 calls and the like. In order to facilitate emergency call handling, E-UTRAN, for example, permits a mobile terminal to select from among a wider number of cells in order to establish an RRC connection for emergency call than those from which the mobile terminal must select for an RRC connection that is to be utilized for purposes other than an emergency call. In contrast to the cells that would be considered suitable to support an RRC connection for purposes other than an emergency call, the cells that are acceptable to support an emergency call include virtually any cell with which the mobile terminal may communicate including those cells operated by different network operators. Accordingly, a mobile terminal generally need not satisfy or have the same access rights in order to utilize the cell for an emergency call, as opposed to otherwise establishing an RRC connection for other purposes with the cell.
Even though a mobile terminal may select from a wider number of cells in order to establish an emergency call as opposed to an RRC connection that is to be utilized for other purposes, it may be desirable to improve emergency call handling in at least certain situations. For example, in E-UTRAN, a mobile terminal may be unable to establish an emergency call while the timer is running during the process of selecting a cell during an RRC connection re-establishment procedure. As noted above, the timer may be set for a predefined length of time, such as 30 seconds, during which the mobile terminal searches for a suitable cell to facilitate re-establishment of the RRC connection. In some instances, a mobile terminal may be unable to identify a suitable cell for purposes of RRC connection re-establishment even though the mobile terminal could readily access one or more cells that would be acceptable for purposes of supporting an emergency call. Thus, a mobile terminal that wishes to establish an emergency call may have to await expiration of the timer in instances in which the mobile terminal is unable to identify a cell suitable for an RRC connection re-establishment even though one or more cells that are acceptable for purposes of supporting the emergency call are available. Such delays in the establishment of an emergency call may be disadvantageous since at least some emergency situations are time sensitive.
In another instance in which an emergency call was established on top of an existing RRC connection, the RRC connection re-establishment procedure may not be able to detect that the emergency call is ongoing since the establishment of the emergency call may be transparent in level 2, e.g., the level in which the RRC connection re-establishment procedure is conducted, and visible only in level 3, e.g., the non-access stratum (NAS) layer, in instances in which an RRC connection already exists that the time of the establishment of the emergency call. For example, a mobile terminal may be operating a background application that requires a network connection such that the mobile terminal has an RRC connection. In instances in which an emergency call is then placed by the mobile terminal, the preexisting RRC connection may not know of or detect the ongoing emergency call since the emergency call may be established on level 3 while the RRC connection utilized by the background application may be supported on level 2. In instances in which the RRC connection is lost and the mobile terminal wishes to recover the RRC connection with a re-establishment procedure, the initiation of the RRC connection re-establishment procedure and its search for a suitable cell with which to re-establish the RRC connection may disadvantageously interrupt the emergency call for an extended period of time.
Also, in instances in which an RRC connection has been established to support an emergency call and another packet data network (PDN) connection is then established in addition to the RRC connection, subsequent efforts to initiate an RRC connection re-establishment procedure may not be able to detect if the emergency call is ongoing. In this regard, in instances in which the emergency call has terminated while the PDN connection that is utilized for other purposes is ongoing, a subsequent RRC connection re-establishment procedure, such as to re-establish the PDN connection that was lost, may consider the emergency call to be ongoing and may select a cell that is acceptable for purposes of supporting an emergency call, but is not suitable for RRC connection re-establishment since, for example, the mobile terminal may not have appropriate access rights to utilize the cell for a PDN connection for purposes other than an emergency call. In this regard, efforts by the mobile terminal to re-establish an RRC connection utilizing a cell that is acceptable for purposes of supporting an emergency call, but that is not necessarily suitable for supporting RRC connection re-establishment for purposes other than an emergency call is likely to fail in that the cell will not have context data associated with the mobile terminal, as is required in order to successfully re-establish an RRC connection. Selection of a cell that is acceptable for purposes of supporting an RRC connection for an emergency call, but not necessarily suitable for RRC connection re-establishment for purposes other than an emergency call may delay the mobile terminal from successfully re-establishing the RRC connection, at least until the mobile terminal performs another search of cells on all frequencies on all radio access technologies (RATs). Moreover, by failing to re-establish the RRC connection with the cell that is otherwise acceptable for purposes of supporting an RRC connection for an emergency call, the efforts to re-establish an RRC connection may fail so as to further delay efforts by the mobile terminal to recover from radio link issues, such as those which caused the initial RRC connection to be lost.